Silver image transfer polymerization process



United States Patent 3,194,661 snzvnn IMAGE TRANSFER POLYMERIZATIUN rnocnss Abraham Bernard Cohen, Springfield, Null, assignor to E. I. du Pont de Nemours and Company, Wilmington, Deh, a corporation of Delaware No Drawing. Filed Feb. 2, 1961, Ser. No. 36,598 23 (Ilaims. (Cl. 96-48) This invention relates to photography and more particularly to processes for the transfer of photographic images. It also relates to novel photographic elements useful in accordance with such processes.

In a conventional silver halide photographic process a latent silver image is produced by the direct action of light or other radiation on sensitized silver halide crystals dispersed in a suitable binder. image is amplified through a chemical or physical development process in order to obtain a useful image. The efiiciency of a photographic system can be expressed by its quantum yield, i.e., the number of elementary reactions corresponding to one light quantum absorbed by the system. The photographic elementary process, i.e., the formation of the latent image, has a quantum yield of less than 1. The developing step increases this quantum yield to to 10 in other words, for each light quantum absorbed in the system 10 to 10 silver atoms are developed in the processed image.

The decomposition of peroxygen compounds by silver (reaction 3 given below) is used in the so-called peroxide-etch process in which a photographic silver image is treated with a peroxide and then washed to give a relief image. This process has a low degree of amplification and depends on the silver catalyzed oxidation of gelatin (or in effect a degradation) to yield a negative relief image. This result is exactly contrary to that of the present invention in which a positive relief is obtained through addition polymerization.

Metal ions, including silver ions, have been widely used to catalyze peroxide initiated polymerizations. But all such processes operate in solutions for bulk polymerization, and no process is known which utilizes metallic silver rather than silver ions and accomplishes a selective, imagewise polymerization in solid phase.

in non-silver halide systems, the quantum yield is usually much lower because no amplification step occurs. Processes like those utilizing diazonium compounds or bichromated colloids provide a quantum yield of approximately 0.5. Exceptions are those processes in which the primary exposure initiates a chain reaction such as in an addition photopolymerization, where the photolytic activation of one monomer molecule can result in a polymer chain having many units of the original monomer. In these cases, the over-all quantum yield is considerably higher than in other non-silver halide processes, but it is generally still far below the over-all quantum yield attainable in silver halide photography.

In practice, a difference in quantum yield usually manifests itself primarily in a difference in photographic sensitivity or speed. Other factors, like image structure and covering power, however, have an effect on the quantum yield-speed relationship.

For many applications of photography it is desirable to have still higher photographic speeds than those that are attainable with the present-day silver halide systems. Such applications include, for example, high speed motion picture photography, low-dosage X-ray recording, available light and subdued light photography, oscillographic recording, astrophotography including photographing artificial satellites, etc. It is also desirable for many purposes to produce images of higher covering power than are attainable with silver images, as well as images Generally, this latent giddfihl Patented July 13, 1965 ice varying in relief or in the degree of moisture sensitivity or permeability for photomechanical purposes. Although processes for the latter applications are known (tanning development of silver halide-colloid systems, dichromate or diazonium sensitized colloids, etc.) their over-all quantum yield is no higher and usually much lower than that of the corresponding parent photosensitive system.

It has been proposed to use silver nitrate or silver halide to initiate a photopolymerization reaction, imagewise (Phot. Sci. and Eng, 4, 151 (1960) and Belgian Patent 582,912), but the proposed processes are slow in comparison with conventional silver halide or photopolymerization processes utilizing organic photoinitiators. It has also been claimed that the over-all quantum yield in silver halide photography can be increased by a factor of 10 by utilizing the serniquinone intermediates produced in photographic development to initiate polymerization (Nature, Dec. 7, 1959, p. 1275). In the examples given, however, the polymerization only serves to modify the state of aggregation and thus the covering power of the silver image, but no true increase in terms of amount of reduced silver is achieved.

An object of this invention is to provide new and useful processes for the formation of photographic images. Another object is to provide simple and dependable processes for transferring photographic images to images of greater density. A further object is to provide such processes which do not require expensive or unique processing equipment. A still further object is to provide such processes which use commercially available materials. A still further object is to provide such processes which can be carried out in a short time by the ordinary technician. Still further objects will be apparent from the following description of the invention.

The silver image transfer-polymerization process of this invention, in its broadest aspect comprises subjecting a developed silver image, while it is in image transfer relationship with a solid stratum comprising a nongaseous, addition polymerizable, terminally ethylenically unsaturated compound, to the action of a peroxygen compound under aqueous conditions at pH below 8 to form silver ions and free radicals until an image of addition polymer is formed in said stratum and removing addition polymerizable compound in the non-image areas.

Where the silver image is in the same stratum as the ethylenically unsaturated compound or is in an adherent layer contiguous therewith, removal of the ethylenically unsaturated compound i accomplished by treating it with a solvent therefor, e.g., by washing or spraying and this treatment will also remove any silver salt, binding agent or filler for the original salt or for the unsaturated compound, pigment, etc. present in the non-polymerized image areas. The silver image-bearing stratum usually will be very thin and of the same order of magnitude as in a conventional photographic film having a gelatin silver halide emulsion layer (i.e., about 0.1 to 10 mils in thickness).

In the case where the silver image is in a separate photographic silver halide emulsion layer, the latter will be in contact with a solid layer comprising the ethylenically unsaturated compound on a separate support, e.g., film plate or paper. The two layer will be in surface contact during the image transfer addition polymerization reaction.

After the polymer image is formed, the two layers are separated, thus removing the addition polymerizable compound from the silver image in the other layer but leaving it in the stratum of the separated layer containing the polymer image. In a subsequent treatment, the addition polymerizable compound in the non-polymer image areas can be removed by washing and/or dissolvin assignees U.S. applications Ser. No. 850,522 filed- Nov. 3, 1959, U.S.P. 3,060,025, Oct. 23, 1962, Ser. No. 839,304 filed Sept. 11, 1959, U.S.P. 3,060,024, Oct. 23, 1962 and 831,700 filed Aug. 5, 1959, U.S.P. 3,060,023, Oct. 23, 1962.

The non-gaseous, addition polymerizable, terminally ethylenically unsaturated compound used in the solid stratum described above may contain 1 to 4 terminal ethylenic groups, have a boiling point above 80 C. at atmospheric pressure, be capable of rapidly forming an insoluble high polymer by free radical-initiated chain propagating addition polymerization in the presence of an addition polymerization initiator therefor. The unsaturated compound, preferably a monomer, may be either liquid or solid but if liquid, a solid inorganic or organic filler material should be present in such an amount that the layer is solid. Suitable photopolymerizable strata and elements of this type for use in the image transfer-polymerization of the invention are described in U.S. Patents 2,760,863, 2,791,504, 2,892,716, 2,893,868, 2,902,365, 2,923,673, 2,927,022, 2,927,023, 2,929,710, 2,948,611 and 2,951,758 and their foreign counterparts.

When the final polymer imagobearing element is to be used in a thermal image transfer process the solid stratum should be solid below 40 C. and thermally transferable by having a stick or transfer temperature above 40 C. and below 220 C. and comprise (a) a thermoplastic organic polymer solid at 50 C. and (b) an ethylenically unsaturated compound containing 1-4 terminal ethylenic (CH =C groups having a boiling point above 100 C. at normal atmospheric pressure, being capable of rapidly forming a high polymer by free radical initiated addition polymerization, as stated above, and also having In carrying out the processof this invention, an enormous increase in quantum yield of the image is obtained.

- This increase is quite unexpected because the main ama plasticizing action on said thermo-plastic polymer; said constituents (a) and (b) being present in amounts from 3 to 97 and 97 to 3 parts by weight respectively. Any of the elements and thermoplastic polymers given in assignees U.S. application Serial No. 831,700 filed August 5, 1959 (U.S.P. 3,060,023, Get. 23, 1962), can be used for the silver image transfer addition transfer'processes of the present invention.

According to a preferred aspect of the invention, a radiation sensitive photographic element having a light sensitive colloid-silver halide emulsion layer is exposed, imagewise, to radiation to produce a latent silver image. The exposure is carried out to such an extent that the silver image after conventional photographic development is substantially above the normal fog level but the layer may still be substantially underexposed. The exposed developed silver image layer is then brought into contact with the polymerizable layer of a separate polymerizable element containing water and a peroxygen compound, particularly a persulfate compound.

The process is preferably carried out by applying the transfer solution to a surface of one of the two layers, i.e., the silver image-bearing layer or the photopolymerizable layer. This transfer solution will generally contain water, a peroxygen initiator, an acid to lower the pH below 8, preferably below7, and a thickening agent to increase the viscosity of the solution and to facilitate spreading of the solution uniformly over the entire transfer area. Solutions having a viscosity of 10 to 300 centipoises are useful. The thickening agents used in adjacent layer or contact development of exposed silver images to form developed silver images in separate silver halide layers are useful in the transfer solutions. Polyethylene oxide, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, polyvinyl alcohol, polyvinyl pyrrolidone, glycerine, and ethylene glycol, diethylene glycol and their derivatives are useful thickening agents.

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plification reaction which takes place in other processes takes place only in a solution system under ideal conditions, whereas the process of this invention embodies a solid, image-forming system. The process of this invention is designated as a silver image-transfer polymerization process because a polymerization reaction is initiated by diffusion of silver ions into the sites of polymerization and while the theory of the reaction has not been fully established, the results might'be explained, Where a persulfate is used as the peroxygen compound and alkyl acrylate as the unsaturated monomer, by having the following series of schematic equations:

(1) light Quantum yield AgBr Ag (latent image) e 51 g Developer Ag (latent image) AgBr 'Ag (image) 10 -10" Ag (image) S10v A3 2804- [3a.Ag13r 8203- No reaction (non-image areas)] (a Ag+ slot- Ag soi.'+ soi- Quantum yield (5) A 1120 Ag -0H 11+ 10 C O O R on nen,=cncoon -cn,( :rr

(7) C 0 OR $0 nCH =OHCO0R- (OHg( H- lO -lO (8) a C O O R A similarsequence of reactions is believed to'take place with other peroxygen compounds. 1

In a simple application of the process, a low density silver image produced by underexposing a photographic silver halide layer to light and by conventional processing (Equations 1 and i2) is brought in contact with a layer containing vinyl monomer, a binder, a persulfate and a high covering power pigment. After separating the two layers and washing out the unpolymerized areas, a high density pigment image of the original underexposed silver image is obtained in the second layer.

In the process, the persulfate ion migrates tothe silver image and converts it to silver ion (Equation 3) which, in turn, grates back to the polymerizable element and decomp ses the persulfate in the presence of the vinyl monomer (Equations 4 and 5). The free radicals thus produced initiate the polymerization of the. monomer (Equations 6 and 7). The over-all reaction, as far as starting material and end product are concerned, and the enormous quantum yieldassociated wi-ththe over-all reaction, are summarized in Equation 8. The cumulative quantum yield obtained in accordance with the invention is quite urprising but it is even more surprising that the reactions (Equat-ions3 7) which involve ratedetermining diffusion steps can be completedin a matter of secends at room temperature.

The increase in effective quantum yield obtained With this invention can be illustrated by the following test: A sensitometric step wedge Was printed on a high speed negative film. After processing, the optical density of the various steps ranged from 0.05 above fog to 2.60 above fog in 18 steps. The highest density step had received 512 times the exposure of the lowest density step. This film was then used to prepare a polymer image in the manner described later in Example I. The density of the polymer image was 2.80 and was uniform from the first step to the last step. Thi means that the step which was underexposed by a factor of 512 gave as good an image as a correctly'exp-osed step. It should be notedhere that the photographic fog, i.e., uncontrollably and spontaneously developed silver which has an optical density of about 0.10 in a high speed negative emulsion, did not result in a corresponding polymerization of the image layer. This is thought to be caused by the fact that the fog silver is distributed uniformly throughout the photographic layer, while the image silver is concentrated near the surface of the layer. Therefore, the silver ion concentration necessary to catalyze the polymerization reaction is not reached in the ffog areas of the photographic layer.

The invention also provides new products, one of such is an image-yieldin element comprising a sheet support bearing on its surface, in either order, a layer of radiation-sensitive silver salt, e.g., silver halide in a waterpermeab-le binder and a solid layer or stratum as described above containing the non-gaseous, addition polymerizable terminally unsaturated compound and a polymeric binding agent.

Another useful product of the invention comprises a support bearing a single layer comprising the radiationsenistive silver salt, the non-gaseous unsaturated compound and at least one polymeric binding agent for one or both of said components, e.g., a Water-permeable macromolecular organic colloid.

Many variations of the basic process outlined above are possible. A number of such variations are covered by the following examples, others will be apparent to those skilled in the art. Therefore, these examples only serve to illustrate, but in no way to limit the scope of this invention.

Examplel A dilute, aqueous carbon black dispersion was prepared according to a process described in US Patent 2,581,414 by rapidly stirring 52 grams of a mixture of a 40% aqueous dispersion of carbon black having an average particle size of 41 m 340 ml. of distilled water and 340 grams of 20 to SO-mesh ()ttawa sand as referred to in A.S.T.M Specification C-i90. After 5 minutes of stirring at room temperature in a stainless steel can of approximately 1500 ml. capacity, the sand was separated from the mixture by filtration through a layer of felt of about inch thickness.

A 40-ml. portion of the filtrate was added to 400 ml. of a solution containing 8% of photographic grade gelatin and 20% of methanol, kept at 30 to 40 C., and 15 m1. of a 5% aqueous solution of a surface active agent (the sodium salt of technical lauryl alcohol sulfate), were added to the gelatin-carbon dispersion.

A coating solution was prepared as follows:

Gelatin-carbon dispersion ml 100 Potassium persulfate solution, 1.33% ml 100 Polyethylene glycol diacrylate g 6.65

This coating solution was coated at about 35 C. on polyethylene terephthalate film made according to Alles et al. US. Patent 2,627,088 and Alles US. Patent 2,779,684, consisting of a polyethylene terephthalate film having a coating of vinylidene chloride/acrylic ester/ itaconic acid copolymer and, over this coating, a thin (0.5 nag/din?) coating of gelatin. After drying, the gelatincarbon black coating had a thickness of about 0.0005 inch.

A photographically processed, i.e., developed and fixed, line and halftone negative was lightly brushed with a transfer solution composed of 1 ml. of 2-molar sulfuric acid and 10 ml. of .a 2% solution of polyethylene oxide characterized by having a molecular weight of about 100,000 and a viscosity, in a 5% aqueous solution, of 225-375 centipoises at C. The so treated negative was brought into intimate contact with the gelatin-carbon black layer by passing the two film between rubber rollers under a slight pressure, and placed in a vacuum frame for one minute to assure that intimate contact between the two layers was maintained. It should be noted that no light was used. 0n separation of the two films, the areas of the pigmented gelatin layer that had e been in contact with silver of the photographic negative were found to be converted into a polymerized image. The unpolymerized areas, corresponding to the non-image areas of the negative, were removed by washing for 3 minutes in an agitated water bath kept at 40 C. The resulting pigmented polymer image was a positive copy of the original silver image, i.e., the black areas of the polymer image corresponded to the black areas of the photographic image.

Example 11 A coating similar to that of Example I was prepared except that the potassium persulfate was omitted from the coating solution. The transfer solution with which the photographic silver image Was brushed was composed of a 0.1-molar solution of potassium persulfate in 2% aqueous polyethylene oxide of the type described in Example I. After bringing the so treated silver image into intimate contact with the receptive, carbon black containing, gelatin/polyethylene glycol diacrylate layer and washing out of the unpolymerized areas as described in Example I, a black image on a transparent background was obtained. This image was a positive reproduction of the original silver images.

The photographic image was then again brushed with the transfer fluid and brought into contact with a new polymerizable layer. Another polymer image was obtained. This process was repeated five times; there was no indication of decreasing image quality with an increasing number of transfers.

Example III Polymerized images similar to those obtained in Examples I and II were prepared from lithographic silver images on films which were developed, but not fixed. The silver areas catalyzed the polymerization of the vinyl monomer, whereas the silver halide areas did not catalyze the polymerization. After removal of the unpolymerized areas with warm water, positive images of the silver image (i.e., line and halftone) were obtained.

Example IV A gelatin/polyethylene glycol diacrylate coating containing dispersed carbon black was prepared as indicated in Example II. A light-sensitive lithographic silver halide emulsion in which the AgCl/AgBr ratio was 7:3 was coated over this layer, so that the coating weight was approximately mg. of silver halide per dm. This emulsion coating was performed in red light in order not to fog the light-sensitive, photographic layer. After drying, the silver halide layer was exposed through a photographic line negative, developed for l0 seconds in an aqueous solution containing 22.1 g. of sodium sulfite, 7.2 g. of 2,4-diaminophenol dihydrochloride and 0.32 g. of K'Br per liter, and then fixed in a non-hardening, acid fixer and washed. The element was then placed in a 0.1-molar potassium persulfate solution for two minutes and then washed in water of 40 C. to remove the unpolymerized areas as described in Example I. A polymerized image contiguous to the silver image was obtained.

Example V A polymerized image contiguous to a silver image was obtained in a process similar to the one described in Example IV, except that the fixing operation in the photographic processing was omitted.

Example VI A gelatin/monomer coating containing dispersed carbon black as described in Examples I and II was coated over the emulsion of a photographic film (lithographic type), containing of AgCl and 30% of AgBr. This element was exposed through the film base and processed as described in Example V. After soaking in a potassium persulfate solution and washing in warm water, a poly- .filed September 27, 1960.

merized image was obtained which was contiguous to the silver image.

Example V H A silver chloride photographic emulsion was prepared which consisted essentially of:

Silver chloride g 215 Gelatin g 700 Water g 9.585

Example VIII A coating similar to that of Example Vii was prepared, except that .g. of o-meth'acrylamidophenol, a monomeric cyan color former, were added to 700 g. of the light sensitive, modified emulsion of Example Vll. After exposure, photographic and polymerization processing as described in Example Vll, the image was subjected to a color coupling reaction by treating it with an alkaline solution of p-aminodiethylaniline and potassium ferr-icyanide. The end result was a cyan colored polymer image.

Example IX Example Vlll was repeated, except that the 10 g. of omethacrylamidophenol cyan color former were replaced by 140 g. of an 8% aqueous solution of a polyvinylacetal color former of the type described in Example I of Schoenthaler et al., US. patent application Serial No. 58,636 After exposure, photographic processing, polymerization and color coupling as in Example VH1 a cyan colored polymer image was obtained.

Example X A partial solution-slurry of a magenta color former monomer, l-phenyl-3-metha'crylarnido-5-pyrazolone, dis closed in Firestine and Umberger US. patent application "erial No. 21,959 filed April 13, 1960, was prepared by vigorously stirring 8 g. or" this monomer with a mixture of 80 ml. of acetone and '20 ml. or" ethanol.

The following coating solution was prepared:

8% gelatin in aqueous methanol ml 5% aqueous dodecyl alcohol sulfate (Na salt) rnl 1 Potassium persulfate g 0.2 Magenta color former monomer slurry ml 10 This mixture was agitated vigorously for 5 minutes and coated on the copolymer coated polyethylene terephthalate film base described in Example 1.. The'thickness of the wet coating was 0.004 inch. The coating was dried in air.

A developed and fixed photographic silver image was lightly brushed with an acidified transfer fluid as described in Example I and brought into intimate contact with the color former contain g coating by passing the two sheets between rollers under moderate pressure. The sandwich was then placed in a vacuum frame and kept in intimate contact for 15 minutes. After that time, the two layers were separated. A clearly defined, polymerized, image was visible on the coating which was insoluble in water at 40 C. whereas the unpoiyrnerized areas dissolved under these conditions. less, image was treated with an alkaline solution of paminodiethylaniline containing potassium ferricyanide.

A magenta colored, polymerized image corresponding to the image areas of the silver image was obtained.

The polymerized, color- I 8 Example XI A pigment/ gelatin dispersion was prepared by stirring at 35 to 40 C., 8 g. of Monastral Green pigment (Cl 74,260) in 4-00 g. of an 8% solution of photographic gelatin in 20% aqueous methanol and adding ml. or" a 5% aqueous solution of the sodium salt of technical lauryl alcohol sulfate. This mixture was then'used to formulate the following coatingsolution:

Pigment/gelatin blend g 10 5% aqueous lauryl alcohol sulfate (Na salt) ml 4 6% polyethylene oxide (-see Example 1) ml 20 Polyethylene glycol diacrylate g 2 Potassium persulfate g 0.2

This mixture was coated at 35 C. on polyethylene tercphthalate film base, describedin Example I. A silver transfer polymerization as described in Example I was then performed; On separating the coating and the silver image, the polymer image remained attached to the image areas of the silver image and was stripped completely from the gelatin/pigment coating. Thus, a negative pigment image with respect to the. silver image remained, whereas the silver imageitself was overlaid with a'contiguous pigmented polymer image.

Example XII A dilute carbon black dispersion in isopropanol was prepared by sandmilling, as in Example I, 52 g. of a 15% carbon black dispersion of 9 m average particle size in 340 ml. of isopropanol for 5 minutes at room temperature. After filtering through felt, this dispersion was sed to prepare the following coating solution:

Cellulose acetate butyrate g Polyethylene glycol diacrylate g 27 Carbon black dispersion ml Acetone ml 1312 This mixture was coated on uncoated polyethylene terephthala'te to give a coating thickness of 0.0002'inch. A photographically developed and fixed line image on lithographic film was lightly brushed with a transfer solution consisting of 2 ml. of 18% hydrogen peroxide, 1 ml. of 2-molar sulfuric acid and 15 ml'. of a 2% aqueous solution of polyethylene oxide as described inExample I. The so treated silver image was brought into intimate contact with the above described coating for 5' seconds by placing the sandwich in a vacuum frame; On separation of t e two sheets, the areas that were in contact with the silver image were found to be convened to a polymerized image. The pigmented layer was then covered with a white bond paper and the assembly passed through rollers Example XIII A photographic negative of a pattern with high subject contrast (a clock face having black numbers on a white background) was obtained on a panchromatically sensitized, high speed negative film' by using a'commercial photographic camera. The negative film had an ASA speed rating of 320. The proper exposure for this film under the available room light, determined with an incident light photoelectric exposure meter, was at a shutter speed of of a second and a lens diaphragm setting of f/ 3.5. The actual exposure was made at o of a second and f/ 22 which would be the correct exposure for a photographic film having an ASA speed ratingof approximately 12,500. The negative film was developed for 10 minutes in a commercial metol hydroquinone-borax fine grain developer and fixed for 10 minutes in. a non-hardening sodium thiosulfatefixing solution. After proper'washing and drying, the extremely underexposed negative was brought into contact with a'polymerizable, pigmented layer of the type described in Example 1. Using the transfer technique of Example I, -a duplicate negative of very high contrast was obtained. Enlarged photographic projection prints of high contrast and good quality were made from the duplicate negative on commercial projection printing paper of normal gradation. These prints were comparable in contrast and definition to those obtained from a normally exposed control negative (rated at a speed of ASA 320). Enlarged prints from the original, under-exposed negative rated at a speed of ASA 12,500 showed very low contrast and definition and were not acceptable by the standards of the industry. The negative film had a gelatin-silver halide emulsion layer.

Example XIV A coating solution similar to the one described in Example X was prepared, except that the ml. of magenta color-former monomer slurry were replaced by 1 ml. of a solution of omethacrylamidophenol cyan colorformer monomer in ethanol. This solution was coated at 35 C. on the vinylidene copolymer coated polyethylene terephthalate film base described in Example I. A developed and fixed photographic camera negative, a cont-inuous tone rendition of an indoor scene, was used to make a silver transfer polymerization on the polymerizable transfer layer using the technique described in Example I. After separation of the two layers, the transfer layer was washed for 3 minutes in a solution of 3 parts of ethanol and 1 part of water to remove the unpolyrnerized cyan color-former. The polymerized, colorless image was then developed With an alkaline solution of p-aminodiethylaniline-2HCl containing potassium ferricyanide. A continuous tone, cyan colored, negative image, corresponding to the original silver image, Was obtained, which could be used to obtain continuous tone, black-and-white photographic prints on a suitably sensitized, photographic paper.

In the foregoing examples the polyethylene glycol diacrylate referred to was the diacrylic acid ester of a mixture of polyethylene glycols where the latter precursor had an average molecular Weight of 300.

In the foregoing examples, the polyethylene diacrylate used was a mixture of diacrylates of polyethylene glycols containing an average of 8 ether groups.

The characteristics of the polymer image obtained by this new image forming process can be varied over a wide range by properly selecting the various components of the image forming element. Thus, if maximum contrast is required the pigment used should be dark, preferentially black. A carbon black dispersion is the preferred pigment, but other materials, such as organic and inorganic pigments that are not decomposed or changed by the oxidizing agents used, can be substituted. Pigments of another color than black lead to correspondingly colored polymer images. For some applications, a pigment-free polymer image is sufficient, for example, for offset printing plates where the printing surface is differentiated by hydrophobic and hydrophilic areas. The color and type of pigment have no influence on the process involved so long as no chemical reaction involving the pigment occurs. In general, the pigment will be present in an amount of 2 to 50% based on the total weight of the polymerizable layer.

- The optical density of the polymer image is independent of the silver density of the photographic image; it is determined by the amount and type of pigment or dye added to the polymerizable layer and by the layer thickness. Thus, underexposures of the silver image by a factor of 10 to 10 still can give satisfactory polymer images.

A suitable binder for the polymerizable layeris gelatin, but for some applications other binders are advantageous. The binder used should be permeable to the solvent used for the solution of the peroxygen compound. Thus, in the preferred system, water-permeable binders such as polyvinyl alcohol, polyacrylamide, polyinyl pyrrolidone, cellulose acetate succinate, polyethylene oxides, bone glue, agar-agar, methyl cellulose, or copolymers of hydrophobic vinyl monomers with hydrophilic monomers such as acrylic acid, acrylamide, sodium styrene sulfonate, etc., or certain nylons that are soluble in aqueous systems, for example the alkoxyethyl nylons and the compounds disclosed in Burg, U.S. patent application Serial No. 753,196, filed August 5, 1958 (U.S.P. 3,043,805, July 10, 1962), can be used. Where water-insoluble peroxides are used such as benzoyl peroxide in ethanol, the process operates best with binders which are alcohol-permeable such as cellulose acetate or cellulose acetate butyrate, polyvinyl acetate, polyvinyl butyral, ethyl cellulose, certain nylons, etc. The selection of the binder depends to some degree on the method of development. Thus, if the image is to be developed by Water washout, the binder should be soluble in water or for alcohol washout, in alcohol. Where development is by thermal transfer, a preferred binder monomer combination should have a reasonably low softening point. It is even possible to use no binder at all, by selecting a monomer which in itself is film forming.

The polymerization reaction of this invention depends on an imagewise distributed silver ion catalyst. Generally, these silver ions are formed in situ by reacting a peroxygen compound with a metallic silver image or a silver halide solvent with unexposed silver halide. Any type of light sensitive silver salt system can be used to produce the original silver image, for example, ordinary photographic emulsions containing silver chloride, silver bromide, silver iodide or mixtures thereof or structures containing other light sensitive silver salts, like silver oxalate, silver acetylide, silver azide, etc. They can be sensitive to various radiations, like visible light, ultraviolet or infrared radiation, X-rays, alpha-, beta-, or gamma-radiation, etc., or to mechanical deformation like pressure.

Any polymerizable vinyl compound that is soluble or dispersable in water or in a solvent, for example in ethanol, methanol, acetone, etc., can be used. Such vinyl monomers are, for example, acrylic acid, methacrylic acid, acrylamide, methacrylarnide, methyl acrylate, ethyl acrylate, methyl methacrylate, vinyl acetate, methyl vinyl ketone, Z-methyl-S-vinyl pyridine, styrene, etc. Also, alkylene or polyalkylene glycol diacrylates prepared from alkylene glycols of 2 to 15 carbon atoms or polyalkylene glycols of l to 10 ether linkages, and those disclosed in Martin and Barney, U.S. Patent 2,927,022, issued March 1, 1960, e.g., those having a plurality of addition polymerizable ethylenic linkages, particularly when present as terminal linkages and especially those wherein at least one and preferably most of such linkages are conjugated with a doubly bonded carbon, including carbon doubly bonded to carbon and to such heteroatoms as nitrogen, oxygen and sulfur. Outstanding are such materials wherein the ethylenically unsaturated groups, especially the vinylidene groups, are conjugated with ester or amide structures. The following specific compounds are further illustrative of this class:

Unsaturated esters of polyols, particularly such esters of the alpha-methylene carboxylic acids, e.g., ethylene diacrylate, diethylene glycol diacrylate, glycerol diacrylate, glycerol triacrylate, ethylene dimethacrylate, 1,3- propanediol dimethacrylate, 1,2,4-btanetriol trimethacrylate, 1,4-cyclohexanediol diacrylate, 1,4-ber1zenediol dimethacrylate, pentaerythritol tetramethacrylate, 1,3-propanediol diacrylate, 1,5-pentanediol dimethacrylate, the bisacrylates and methacrylates of polyethylene glycols of molecular weight 200-500, and the like; unsaturated amides, particularly those of the alpha-methylene carboxylic acids, and especially those of alpha, omegadiamines and oxygen-interrupted omega-diamides, such as methylene bis-acrylamide, methylene bis-methacrylamide, ethylene bis-methacrylamide, 1,6-l1examethylene bis-acrylamide, diethylene triamine tris-methacrylamide,

divinyl succinate, divinyl adipate, divinyl phthalate, di-' vinyl terephthalate, divinyl benzene-1,3-disulfonate, and

- divinyl butane-1,2-disulfonate; acrylate salts, such as calcium acrylate, magnesium acrylate, etc; and unsaturated aldchydes, such as sorbaldehyde (hexadienal).

The polymerization initiator is a peroxygen compound. Potassium persulfa'te is the preferred initiator, but other peroxygen compounds are useful, for example, sodium and ammonium persulfate, hydrogen peroxide, benzoyl peroxide, succinic acid peroxide, t-butyl hydroperoxide, sodium perborate, and others.

The polymerization reaction is initiated by contacting the polymerizable layer with a silver image layer in the presence of a peroxy initiator. By adding the initiator to either one of these layers the reaction takes place in an ordinary dry state, for the dry layers contain enough atmospheric moisture that the ionic diffusion can take place. However, the diffusion can be accelerated by moistening either one or both surfaces which yields higher reaction speeds. In this case, the initiator can be incorporated in the transfer ruid.

The initator can be added to the transfer fluid instead of being incorporated in the polymerizable layer. This eliminates any premature decomposition of the highly reactive initiator and therefore increases the shelf life of the polymerizable layer.

The transfer time can vary considerably. Since lateral diffusion can occur and reduce resolution, the time should be kept as short as possible. In one experiment similar to Example ll, contact times of 1, 5, and 15 minutes respectively all yielded comple ely polymerized images but the 1 minute image was much sharper than the 5 minute image which, in turn, was sharper than the minute image.

Sharpness can also be increased by the use of thin layers which minimize lateral diffusion. Since the covering power of the pigmented layers is very high and since the amount of silver required in the light sensitive layer is low, this system lends itself readily to this layers.

In those applications where a silver halide layer and a polymerizable layer are coated one over the other on the same support of Where a suitable vinyl monomer is added to a liquid silver halide emulsion and the mixture coated on a support (Examples V to X) the use of a transfer fluid is not required. However, it is preferred not to incorporate the initiator into the coatings, but rather to treat the exposed, composite coating with a solution of the initiator.

The initiator concentration in the transfer fluid is generally adjusted from Obi-molar to Z-molar, preferably from ODS-molar to 0.2-molar. A higher initiator concentration requires a shorter contact time of the two layers. With some initiators the concentration is limited by their solubility.

If the initiator is incorporated in the gelatin/monomer coating, an amount of l to based on the monomer weight is satisfactory. Usually, 10 to 20% were used, the higher amounts giving more rapid polymerization.

The oxidation of the metallic silver to silver ions by the persulfate ions is favored by an acid medium (see reaction 3, above). Therefore, the addition of acid to the transfer fluid increases the reaction rate which, in turn shortens the contact time between the silver image and the polymerizable layer or the immersion time of the compound layers in the peroxy salt solution.

Many peroxy compounds, however, undergo a hydrolytic dissociation in an aqueousv solution which lowers the pI-l of the solution below the neutral point. In these cases, the initiation reaction takes place in absence of any additional acid. The typical initiators of this type are the persulfates. It should be noted, that the reaction rate with'these initiators, too, is greatly increased by additional acid.

Theutility of the processes and products of this invention have been described in the foregoing text and especially in the examples. The invention, however, is not limited to merely increasing the quantum image yield from developed silver images but as will be apparent to, those skilled in the photographic and related arts, is useful for many practical purposes. For example, the process of the invention can be used in the preparation of lithographic printing plates which are characterized by exceedingly shallow reliefs and by having ink-receptive and ink-repellent areas. By having both hydrophobic materials and hydrophilic materials in respective areas lithoplates can be made. The invention is useful in preparing halftone and line letter-press printing plates as well, Plate production is greatly simplified by the invention. In addition, greater speeds are possible because no photographic exposure of the photopolymerizable plate is necessary.

The process of the invention can be used to prepare resist images for screen printing, for etching, for the preparation of printed circuits, etc. I

Another advantage of the invention is that satisfactory high-contrast oil-set plates can be prepared from lowcontrast silver images and without the intermediate photographic steps often used to increase contrast. Still other advantages will be apparent fromthe foregoing description of the invention.

1 claim:

1. A silver image transfer process which comprises treating a stratum containing a silver image and in which any metal-containing, image-yielding material in association with said stratum and image is a silver-containing material, by subjecting the silver image while said image is in directly adjacent transfer relationship with a stratum comprising a non-gaseous addition-polymerizable ethylenically unsaturated compound containing at least one terminal ethylenic group, to the :actionrof a peroxygen compound under aqueous conditions at pl-l below 8.0 until an image of addition polymer corresponding to the silver image is formed in said stratum.

2. A process according to claim 1 wherein said stratum is solid.

3. A process according to claim l'whereinsaid action is maintained under aqueous conditions below pH 7.

4. A process according to claim 1 wherein the silver image is in the same stratum as the thylenically unsaturated compound. I

5. A process according to claim 1 wherein the silver image is in a separate layer from the ethylenically unsaturated compound. i

6. A process according to claim 1 wherein the silver image is in an outer layer on one support and the ethylenically unsaturated compound is in an outer' layer on a separate support.

7. A process according to claim 1 wherein the addition polymerizable compound is removed, after formation of an image of addition polymer, by means of a solvent therefor. Y

8. A process according to claim 1 wherein said peroxygen compound is a persulfate.

9. A process according to claim ll wherein the silver.

image is in a thin gelatin layer. I

lit. A process according to claim 1 wherein the peroxygen compound is incorporated in said stratum.

11. A process according to claim 1 wherein said stratum contains an addition polymerizable color yielding compound. 7

12. A process according to claim l wherein the addition polymerizable compound is removed by separating the silver image bearing layer from the layer containing the ethylenically unsaturated compound.

13. A process according to claim 12 wherein after separation of thelayers, the addition polymerizable ma- 13 terial in non-polymer image areas is transferred by contacting it with a separate support while subjecting it to a solvent therefor.

14. A process according to claim 12 wherein after separation of the layers the addition polymerizable material in non-polymer image areas is transferred by contacting it with a separate support while subjecting it to heat above the lowest transfer temperature.

15. A silver image transfer-polymerizable process which comprises subjecting a developed silver image in a stratum in which any metal-containing, image-yielding material in association with the developed silver image is a silver-containing material, while the developed silver image is in image transfer relationship with a solid stratum comprising (a) an organic polymer solid at 50 C. and (b) an ethylenically unsaturated monomer containing l-4 terminal ethylenic groups, having a boiling point above 80 C. at normal atmospheric pressure and'being capable of rapidly forming a high polymer by free radical initiated, chain propagating, addition polymerization, wherein constituents (a) and (b) are present in amounts from 3 to 97 and 97 to 3 parts by weight, respectively, to the action of a peroxygen compound under aqueous acidic conditions at a pH below 8.0 to form silver ions and free radicals until an image of addition polymer is formed in said stratum and removing addition polymerizale compound in the non-image areas.

16. A process according to claim 15 wherein the silver image is in the same stratum as the ethylenically unsaturated compound.

17. A process according to claim 15 wherein the silver image is in an outer layer on one support and the ethylenically unsaturated compound is in an outer layer on a separate support.

18. A process which comprises applying to the surface of an addition polymerizable element having a solid stratum comprising a non-gaseous, addition polymerizable terminal ethylenically unsaturated compound anaqueous transfer solution containing a peroxygen initiator compound and an acid to lower the pH below 7; contacting the surface of the treated stratum with a silver image bearing layer in which any image-yielding, metal-containing material in association with the silver image is a silver-containing material and separating the layer and stratum.

19. A process according to claim 18 wherein the aqueous solution has a viscosity of 10 to 300 centipoises.

20. A silver image transfer-polymerization process which comprises subjecting a developed silver image, while it is in directly adjacent image, a stratum in which any image-yielding, metal-containing compound in association with the silver image is a silver-containing material transfer relationship with a solid stratum comprising a non-gaseous, addition polymerizable, ethylenically unsaturated compound containing at least one terminal ethylenic group, to the action of a peroxygen compound under aqueous acidic conditions at a pH below 8.0 to form silver ions and free radicals until an image of addition polymer is formed in said stratum, and removing addition polymerizable compound in the non-image areas.

21. A silver image transfer-polymerization process which comprises treating a stratum selected from the group consisting of:

(a) a stratum containing a silver image as the sole inorganic image-yielding material and (b) a stratum containing a silver image and associated silver halide as the sole inorganic image-yielding materials, while said stratum is in directly adjacent transfer relationship with a stratum comprising a non-gaseous, addition polymerizable ethylenically unsaturated compound containing at least one terminal ethylenic group, by subjecting the silver image to the action of a peroxygen compound under aqueous conditions at pH below 8.0 until an image of addition polymer corresponding to said silver image is formed in said stratum.

22. A process according to claim 21 wherein said stratum is a washed stratum, being free from water-soluble salts.

23. A process according to claim 21 wherein said silver image is a developed silver image and said stratum is a washed stratum, being free from water-soluble salts.

References Cited by the Examiner UNITED STATES PATENTS 2,473,548 6/49 Smith 260-785 3,019,104 1/62 Oster 96-29 3,029,145 4/62 Dumers et al. 96-35 3,031,301 4/62 Agens 96-27 3,038,800 6/62 Luckey et al. 96-35 3,047,422 7/62 Sites et al. -115 3,073,699 1/ 63 Firestine 96-35 References Cited by the Applicant UNITED STATES PATENTS 2,473,548 6/ 49 Smith. 2,473,549 6/ 49 Smith. 3,101,270 8/63 Evans et al.

FOREIGN PATENTS 582,912 10/59 Belgium.

NORMAN G. TORCHIN, Primary Examiner.

PHILIP E. MANGAN, Examiner. 

1. A SILVER IMAGE TRANSFER PROCESS WHICH COMPRISES TREATING A STRATUM CONTAINING A SILVER IMAGE AND IN WHICH ANY METAL-CONTAINING, IMAGE-YIELDING MATERIAL IN ASSOCIATION WITH SAID STRATUM AND IMAGE IS A SILVER-CONTAINING MATERIAL, BY SUBJECTING THE SILVER IMAGE WHILE SAID IMAGE IS IN DIRECTLY ADJACENT TRANSFER RELATIONSHIP WITH A STRATUM COMPRISING UNSATURATED COMPOUND CONTAINING AT LEAST ONE TERMINAL ETHYLENIC GROUP, TO THE ACTION OF A PEROXYGEN COMPOUND UNDER AQUEOUS CONDITIONS AT PH BELOW 8.0 UNTIL AN IMAGE OF ADDITION POLYMER CORRESPONDING TO THE SILVER IMAGE IS FORMED IN SAID STRATUM. 